The present invention relates generally to analog electronic circuits and more particularly to a circuit for implementing nonlinear operators.
Various circuits are known in the prior art for performing Nth-order operations. One such device includes a log-converter, a gain stage (where the gain=k) and an antilog converter to provide the Kth-order function, such that the output V.sub.o is expressed as EQU V.sub.o =.alpha.(V.sub.in).sup.k.
In this case the gain K can be manipulated to yield either a power or a root. However, this method is very complex and requires a temperature compensating component in each converter. Typical circuits using this approach appear in a publication by National Semiconductor, Inc., entitled "Linear Applications", Vol. 1 (1973) at pages AN31-18,20. Another circuit at page AN31-15 of the above reference is a two quadrant multiplier wherein EQU V.sub.o =KV.sub.x V.sub.y.
However, this circuit is only useful for squaring and requires a thermistor for temperature compensation because it operates on the principle of modulating the r.sub.E term, which is equal to KT/qI.sub.E where I.sub.E is one of the inputs. Further, this circuit is not readily adaptable to yield the inverse function, i.e., the square root.
Yet another prior art approach utilizes the square-law characteristics of an MOS device to perform a squaring operation. This approach is extremely susceptible to temperature variation and the uniformity from device to device is generally poor because of the variation in threshold voltage V.sub.T. Again, the inverse function is not possible.
It is a principal object of this invention to provide a versatile Nth-order function converter that is readily programmable to operate as either an Nth-root extractor or an Nth-power operator. Another object of this invention is to provide a high speed analog function converter using bipolar devices in current mode operation. Still another object is to provide an inherently temperature stable converter requiring no external compensation.